1. Field of the Invention
The present invention relates to a device for flushing a deadspace of a mechanically ventilated patient during an expiration phase of artificial ventilation in order to reduce the rebreathing of expired gas.
2. Description of the Prior Art
In the mechanical ventilation of a patient carbon dioxide (CO.sub.2) may collect in the patient's airways during an expiration phase of a breathing cycle. The collected CO.sub.2 then will be re-breathed during the next inspiration phase of the breathing cycle. It is known that CO.sub.2 can be at least partly eliminated from the upper airways by flushing the airways with a flushing gas, preferably a CO.sub.2 -free flushing gas, during at least a final part of the expiration phase. One known device used to flush the airways in this manner is described in a technical note entitled "Expiratory Flushing of Airways: a Method to Reduce Deadspace Ventilation" by B. Jonson et al (Eur. Respir. J 1990, 3, 1202-1205). This device has a source of pressurized gas, being either a standard gas bottle or a mechanical ventilator (for example of the type ServoVentilator 900C from Siemens-Elema AB, Solna, Sweden). The pressurized gas source supplies breathing gas as the flushing gas after the inspiration phase, and is coupled via a controllable valve system to one end of a conduit. The opposite end of the conduit is insertable into the trachea of the patient so that flushing gas may be supplied into the patient's airway. An electronic control unit' is also provided in operable connection between the mechanical ventilator and the valve system and controls the valve system so that flushing gas, either in pulses or as a continuous stream, is supplied into the conduit during the final part of the expiration phase. Acting on timing information provided to it from the control system of the ventilator, the electronic control unit operates the valve system to supply the flushing gas during a final part of the expiration phase, in this case after 50% of the expiration phase has elapsed and until 10% remains.
This known device has the disadvantages that a specialized flushing source is required, either in the form of a source separate from the mechanical ventilator or in the form of a ventilator that can supply breathing gas even during an expiration phase, and that a relatively complex electronic control system is required to regulate the supply of flushing gas to the patient.